FAQ:Why allow zero stretching at all?

DCCWiki, a community DCC encyclopedia.
Jump to: navigation, search
See more FAQs
General information
DCC Categories Beginner
Related Articles:
Zero Stretching in the DCC Waveform

Zero Stretching or Analog Mode is not part of the NMRA DCC Standard.

Some manufacturers added the analog mode to create a compelling reason to adopt Digital Command Control in the early years, as modellers (particularly those with large fleets of motive power) were concerned about the costs of conversion to DCC.

This allowed DC locomotives to be controlled without adding a multifunction decoder. It is not a crucial feature today unlike 30 years earlier when DCC was introduced. It is now a legacy feature that some DCC systems still incorporate.

Analog compatibility mode is only one use for zero stretching. Other possible uses include the following:

  1. Providing a stretched zero after each packet for the purpose of superimposing locomotive feedback to the command station.
  2. Allowing generation of the command control signal with a computer using a standard serial port, which may not be possible without slightly stretching some zeros.
  3. There are probably other uses that will become apparent as time goes on. Note that the above-mentioned uses are still very much in the experimental stages. The point is that preserving the ability to stretch zeros allows for the possibility of some interesting things.